Method for operating a cutting unit between first and second operation modes

ABSTRACT

The present invention relates to a method for operating a cutting unit ( 1 ) that has a cutter bar ( 6 ) that is operated rigidly or flexibly, depending on the harvest conditions, which can be operated in at least two different operating modes, wherein the cutting unit ( 1 ) includes a first sensor assembly ( 1 ) disposed on the cutting unit ( 1 ) that can be deactivated, which is for operating the cutting unit ( 1 ) in a first operating mode, and a second sensor assembly ( 17 ) for operating the cutting unit ( 1 ) in a second operating mode, wherein, when switching between the at least two operating states, the first sensor assembly ( 13 ) or the second sensor assembly ( 17 ) is activated without interruption in operation, to execute a distance determination, depending on the selected operating mode.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. DE 102016 124 552.6, filed Dec. 15, 2016, the entire disclosure of which ishereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a method for operating a cutting unithaving a cutter rigidly or flexibly operated cutter bar, and to acutting unit and combine harvester having such a cutter bar.

BACKGROUND

It is known from the prior art to operate cutting units equipped withconveyor belts for harvest transport, so called drapers, having a rigidor flexible cutter bar, in at least two operating modes, depending onthe harvest conditions. For harvesting grain, the cutting unit is guidedover the ground with rigid cutter bars at a preset cutting height, i.e.a predefined height setting. Changes in the distance between the groundand the cutter bar of the cutting unit are reacted to, such that thecutting unit is continuously adjusted in terms of its distance to theground. For this, the cutting unit has a first sensor assembly, whichcan be deactivated, that is disposed on the cutting unit, for operatingthe cutting unit in this first operating mode. The first sensor assemblyis formed by numerous sensor arms or bands disposed on the undersurfaceof the cutting unit, which are disposed directly behind the cutter bar.

A second operating mode is the flexible operation of the cutter bar,which lies on the ground in order to follow the contour of the ground,while the cutting unit frame of the cutting unit is guided at apredefined distance from the ground. For this, the cutting unitcomprises a second sensor assembly for operating the cutting unit in thesecond operating mode.

Switching between these two operating modes requires the deactivation ofthe first sensor assembly, e.g. by removing the sensor bands or throughthe manual transferring of the sensor bands into a parking position, andthe subsequent calibration of a control device by means of which anactuating element is activated, which maintains a constant spacingbetween the cutting unit, or cutting unit frame, and the ground.Switching from the first operating mode to the second operating mode andback is time consuming due to the manual deactivation, or activation,respectively, in each case accompanied by an interruption in theoperation thereof, and the calibration process that is to be carriedout.

SUMMARY

The disclosed embodiments provide a method for operating a cutting unit,and to provide a cutting unit, in order to be able to react moreflexibly to changing harvest conditions.

In one embodiment, it is proposed that when switching between the atleast two operating modes, depending on the selected operating mode, thefirst sensor assembly or the second sensor assembly is activated withoutinterrupting the operation thereof in order to determine the spacing.The method provides for the simultaneous operation of both sensorassemblies, wherein, in accordance with the selected operating mode,only the sensor signals supplied by the first sensor assembly or thesecond sensor assembly are processed in order to adjust the height ofthe cutting unit. As a result, it is not necessary to manuallydeactivate the first sensor assembly disposed on the cutting unitthrough the removal or the transferring thereof to a parking position,in order to switch from the first to the second operating mode, as isnecessary according to the prior art, requiring an interruption in theoperation thereof. The same applies when switching from the second tothe first operating mode, which is likewise carried out withoutinterruption of the operation, while according to the prior art, thisrequires that the sensor bands be reinstalled, or returned from theparking position.

The first sensor assembly can be configured as a mechanical groundsensing device, comprising, e.g., sensor bands, sensor skids, or thelike. Alternatively, the first sensor assembly can also be configured asa device that functions without physical contact, which detects thedistance to the ground. The second sensor assembly can be configured asa device integrated in the cutting unit, in particular the cutting unitframe, which detects the distance to the ground directly or indirectly.The method makes it possible to switch between the at least twooperating modes during the harvesting process, in order to be able toquickly and flexibly react to changes in the harvest conditions, withoutinterrupting the harvesting process. The manual deactivation of thefirst sensor assembly, as well as the recalibration of the first orsecond sensor assembly after a manual activation of the first sensorassembly, is eliminated when changing operating modes. The method can beused for belt cutting units as well as for grain cutting units withflexible cutter bars.

It is advantageous that the calibration is carried out for the firstsensor assembly and the second sensor assembly independently of theselected operating mode. The calibration of the first sensor assemblyand the second sensor assembly can be carried out sequentially thereby.For this, the calibration can be initiated after installation on aharvester, in particular on a combine harvester, in order to calibratethe first sensor assembly and the second sensor assembly. The presenceof the first sensor assembly on the cutting unit can be checked in anupstream step thereby. Furthermore, in a preceding step, the cutter barcan be automatically hydraulically released. For the calibration, theupper and lower limits of position sensors of the first and furthersensor assemblies can be determined. The data obtained through thecalibration are stored in a control device, such that they are availableat all times when switching between the operating modes.

Alternatively, the calibrations of the first sensor assembly and thesecond sensor assembly can be carried out independently. This means thatthe calibration is first carried out for only the second sensorassembly, because, e.g., an at least partially releasable first sensorassembly is not disposed on the cutting unit when the calibration isinitiated. Accordingly, after the first sensor assembly is attached, thecalibration thereof can be carried out separately. As explained above,the data obtained for the first sensor assembly and the second sensorassembly by means of the calibration process are stored in a controldevice, such that they are available at all times when switching betweenthe operating modes.

In particular, the first sensor assembly can be activated in the firstoperating mode, in which the cutting unit is operated with a rigidcutter bar, by means of which a predefined height adjustment of thecutting unit is controlled or regulated. In order to rigidly operate thecutter bar, it can by hydraulically tensioned by means of an actuatorelement.

Furthermore, the second sensor assembly can be activated in the secondoperating mode, in which the cutting unit is operated with a flexiblecutter bar, by means of which a predetermined height adjustment of thecutting unit frame of the cutting unit can be controlled or regulated.For a flexible operation of the cutter bar, this can be hydraulicallyreleased through an appropriate activation of the actuator element.

Thus, during the harvesting process in the first operating mode, inwhich the cutter bar is operated rigidly, in order to harvest uprightgrain, it may be the case that there are deposits between the uprightgrain, which require a cut directly above the ground, i.e. below thepreset cutting height. For this, it is possible to switch from the firstoperating mode to the second operating mode, in which the cutter bar isoperated in a flexible manner, in order to lay the cutter bar on theground while the cutting unit frame is guided at apredefined/predefinable distance to the ground. In this situation, thefirst sensor assembly is deactivated, i.e. the signals generated by thefirst sensor assembly are not processed for regulating the distance tothe ground. Instead, when switching to the second operating mode, thesecond sensor assembly, which has been inactive until then, isactivated, in order to process signals generated by the second sensorassembly, which are used to regulate the spacing, or control the height,respectively, of the cutting unit. The two sensor assemblies canfunction in an overlapping manner, such that a quick switch betweenoperating modes, and a combining thereof, are possible. In order toimprove the process flow, it is also possible to incorporate a loadrelief system for the flexible cutter bar in the control or regulatingprocess.

Preferably, with an operation of the cutting unit above the predefinedheight setting of the cutter bar, it is possible to switch automaticallyto a rigid state, independently of the selected operating mode. This isuseful, for example, upon reaching a headland, because the cutting unitis raised at this point. This ensures an optimal, or minimal spacingbetween the reel and the cutting unit table, and allows the reel tosupport the crop flow in an optimal manner.

Furthermore, in an operation of the cutting unit with a flexiblyoperated cutter bar above the predefined height setting, the firstsensor assembly is activated in a time-dependent manner. This isadvantageous when, at the end of a headland the cutting unit is placedback in the field that is to be harvested, because the first sensorassembly already comes in contact with the ground, before the secondsensor assembly can generate a signal.

In particular, the cutter bar can be switched automatically to aflexible state when the cutting unit is operated below a threshold valueof the predefined height setting, independently of the selectedoperating mode.

Moreover, when the cutting unit is operated with a flexibly operatedcutter bar below a threshold value of the predefined height setting, thesecond sensor assembly can be operated in a time-dependent manner. Thisfunction likewise supports the placement of the attachment back into thecrop, because the cutter bar is first released just above the ground. Asa result, crop lifters disposed on the cutting unit, for example, areplaced at the correct angle to the ground, instead of at a steep angle,which is obtained with the abrupt release of the cutter bar and exposesthem to the risk of damage when they are placed back into the crop.

In another aspect, a cutting unit that has a cutter bar, which can beoperated rigidly or flexibly by means of an actuator element, dependingon the harvest conditions, wherein the cutting unit can be operated inat least two different operating modes, and the cutting unit includes afirst sensor assembly disposed on the cutting unit, that can bedeactivated, which is for operating the cutting unit in a firstoperating mode, and a second sensor assembly for operating the cuttingunit in a second operating mode. The cutting unit is connected to acontrol device, which is configured to activate the first sensorassembly or the second sensor assembly, without interruption of theoperation, when switching between the at least two operating modes,depending on the selected operating mode, in order to determine adistance to the ground. The cutting unit can preferably include thecontrol device. This has the advantage that when the cutting unit isused differently with other harvesters, the method according to theinvention can be implemented independently of an additional control unitof the harvester. Irrespective of this, the control device can also be acomponent of the harvester with which the cutting unit is operated. Thecutter bar is disposed on supporting arms, which are pivotally hinged tothe main frame of the cutting unit. By means of the actuator element,which comprises a hydraulic cylinder dedicated to the respective supportarm, the cutter bar can be operated in a rigid or flexible mannerthrough an appropriate change in the pressure applied by this actuatorelement. The calibration data from the first sensor assembly and thesecond sensor assembly necessary for switching operating modes withoutinterruption are preferably stored in the control device.

The first sensor assembly can include at least two devices that sensethe ground, which are disposed on the side of the cutting unit facingtoward the ground. Such ground sensing devices, which are releasablyattached to the cutting unit, can be sensor bands, sensor skids, orother means that mechanically sense changes in the ground contour.Alternatively, the ground sensing device can also be configured as adevice that functions without physical contact.

In particular, the second sensor assembly can be configured fordetecting a pivotal movement, caused by the support arms supporting thecutter bar. For this, the second sensor assembly can be integrated inthe cutting unit.

Moreover, the control device can be configured to activate the actuatorelement, by means of which the cutter bar can be operated in a rigid orflexible manner. This enables a quick switching between the operatingmodes.

Furthermore, a combine harvester may have a cutting unit according toany of the preceding embodiments, which can be operated, in particular,by a method according to any of the preceding embodiments. A combineharvester that has such a cutting unit allows for a simple switchingbetween the at least two operating modes, without requiring a manualdeactivation of the first sensor assembly prior to switching operatingmodes. The calibration effort is also eliminated in a respectiveswitching between the operating modes.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention shall be described in greater detail below, basedon exemplary embodiments depicted in the drawings.

Therein:

FIG. 1 shows a schematic view of a cutting unit;

FIG. 2 shows a partial view of the cutting unit according to FIG. 1;

FIG. 3 shows a flow chart illustrating a calibration process; and

FIG. 4 shows a flow chart illustrating operating states and transitionsbetween the operating states.

DETAILED DESCRIPTION

The illustration in FIG. 1 shows a schematic depiction of a cutting unit1. The cutting unit 1 has a main frame 2, on which a middle section 3and at least two side sections 4, disposed adjacent to the middlesection 3, are disposed. A cutter bar 6 is disposed on the middlesection 3 and the side sections 4 on the front surface of the cuttingunit 1 lying opposite the main frame 2, which extends substantially overthe entire width of the cutting unit 1. Reels (not shown) are disposedon the main frame 2 of the cutting unit 1, which extend over the widthof the side sections 4 as well as in part over the width of the middlesection 3. The reels serve to improve the receiving of the harvest bythe cutter bar 6.

The harvest separated by the cutter bar 6 is fed to a conveyor 5disposed behind the cutter bar 6, which is formed on the respective sidesections 4 as at least one continuous, revolving belt 7, which revolvesparallel to the longitudinal axis of the cutting unit 1. The continuousrevolving belts 7 are disposed adjacent to the middle section 3, inorder to transport the harvest cut by the cutter bar 6 parallel to thelongitudinal axis of the cutting unit 1, toward the middle section 3,and to feed the harvest into a feed device. The middle section 3likewise comprises a conveyor 5 configured as a continuous revolvingconveyor belt 7 a. Other designs for the conveyor 5 in the middlesection 3 are also conceivable. The feed device 8 is configured as afeed roller 9 that can be driven. The feed device 8 conducts the harvestsupplied from the side by the continuous belts 7 to the middle section 3into an opening provided behind the feed roller 9 in the main frame 2,through which the harvest is supplied to the combine harvester forfurther processing through a feed channel 10, to which the cutting unit1 is releasably attached, which is located on a, not shown, combineharvester.

The illustration in FIG. 2 shows a partial view of the cutting unitaccording to FIG. 1. Support arms 11 are hinged to the main frame 2 suchthat they can pivot over a horizontal axis. The cutter bar 6 is disposedon the support arms 11. An actuator element configured as a hydrauliccylinder 12 is dedicated to each support arm 11, with which therespective support arm 11, and together therewith, the cutter bar 6, canbe operated in at least one first operating mode and one secondoperating mode. In the first operating mode, the cutter bar is operatedrigidly. For this, the hydraulic cylinders 12 are subjected to ahydraulic pressure greater than a first threshold value, such that theindividual support arms 11, and together therewith, the cutter bar 6,are unable to pivot vertically. The cutting unit 1 is guided to apredefined distance from the ground. In order to control or regulate thedistance with respect to the cutting height, the distance between thecutting unit 1 and the ground is detected by a first sensor assembly 13.

In the second operating mode, the cutter bar 6 is operated flexibly. Forthis, the hydraulic cylinders 12 are subjected to a hydraulic pressurebelow a second threshold value, such that the cutter bar 6 lies on theground with a weight that is a function of the pressure. With a changein the ground contour followed at least in part by the cutter bar 6, thesupport arms 11 are deflected vertically. The vertical deflection isdetermined by means of a second sensor assembly 17.

A third operating mode provides for the flexible operation of the cutterbar 6 and the conveyors 5 of the side sections 4 disposed downstream ofthe cutter bar. In this third operating mode, the cutter bars 6 and thecontinuous revolving belts 7 follow the changes in the ground contour,which are detected by the second sensor assembly 17.

The first sensor assembly 13 is configured as a ground sensing device.This comprises sensor bands 14, sensor skids, or the like, each of whichare disposed at one end, at a bearing point 15, on at least two supportarms 11 of the cutting unit 1, such that they can pivot over ahorizontal pivotal axis 16. Each side section 4 preferably has at leasttwo sensor bands 14, which are spaced apart from one another. With achange in the ground contour, which results in a change in the distancethereto, the deflection of the respective sensor band 14 over a pivotalaxis 16 is detected by means of a potentiometer dedicated thereto. Thesignal supplied by the potentiometer is evaluated by a control device 50dedicated to the cutting unit 1, in order to carry out a correctioncorresponding to the change in distance, so that the predefined heightsetting, or cutting height, can be maintained. The control device 50 isconnected to the sensor assemblies 13 and 17 by means of a signal line51. The sensor bands 14 are releasably disposed to the support arms 11,such that they can be replaced if necessary.

The second sensor assembly 17 is configured to detect the pivotalmovement caused by the support arm 11 of the cutting unit 1 supportingthe cutter bar 6, when the cutting unit 1 is operated in the secondoperating mode. The second sensor assembly 17 comprises a shaft 18,which extends substantially over the entire width of the respective sidesection 4. The shaft 18 is rotatably supported in consoles 19 dedicatedto the support arms 11. Furthermore, a lever assembly 20 is provided,through which the shaft 18 is connected to the respective support arms11. The vertical deflection of the support arms 11 when there is achange in position is transferred by the lever assembly 20 to the shaft18 as a rotational movement. The greatest vertical deflection of asupport arm 11 at a side section 4 results in the greatest rotation ofthe shaft 18, which is drawn on as a signal that is to be assessed foran automatic height adjustment of the cutting unit 1. For this, thecutting unit 1, which is disposed on the feed channel 10 of the combineharvester, is adjusted in terms of its height by corresponding hydrauliccylinders disposed on the feed channel 10 and the combine harvester,such that the distance of the main frame 2 to the ground is nearlyidentical at all side sections 4.

The cutting unit 1 is to be operated such that when switching betweenthe at least two operating modes, the first sensor assembly 13 or thesecond sensor assembly 17 is activated without interruption in theoperation, depending on the selected operating mode, in order to executea distance determination. For this, the first sensor assembly 13 and thesecond sensor assembly 17 must be calibrated prior to starting theharvest process. The data obtained through the calibration are stored inthe control device 50 such that they can be accessed.

A flow chart illustrating a calibration process or learning process isdepicted in FIG. 3, in which the first and second sensor assemblies 13,17 are calibrated in the calibration process. The calibration processtakes place thereby, independently of the selected operating mode. Forthis, it is checked in step 21 whether the first sensor assembly 13 isdisposed on the cutting unit 1. Independently of the presence of thefirst sensor assembly 13, in step 22 the actuator element configured asa hydraulic cylinder 12 is automatically activated by the control device50, in order to release the cutter bar 6. In the following steps 23 and24, both the upper and lower threshold values for the second sensorassembly 17, for the deflection of the cutter bar 6, as well as theupper and lower threshold values for the first sensor assembly 13, forthe deflection of the sensor bands 14, are learned, as long as thesesensor assemblies have been attached to the cutting unit 1. For this,the determined calibration data are stored in the control device 50 suchthat they can be accessed. When the calibration data for the two sensorassemblies 13 and 17 are obtained, a switching of operating modes can becarried out at any time, without having to recalibrate.

In the following, it shall be described by way of example how anoperating mode switch can be carried out while the cutting unit 1 is ina harvesting mode, after a one-time calibration has been carried out. Itshall be assumed that the initial operating mode is the first operatingmode, which embodies the operation of the cutting unit 1 with a rigidlyoperated cutter bar 6, which is used for harvesting stalk-type crops,such as grain. An operator determines a cutting height in the frameworkof this operating mode. The cutting height is maintained based on thechanges in distance to the ground determined by means of the firstsensor assembly 13.

The second sensor assembly 17 is deactivated, i.e. the control devicedoes not process signals recorded by the second sensor assembly 17.

When the harvester reaches a crop deposit, i.e. stalk-type harvest lyingon the ground, the preset cutting height of the first operating modedoes not enable harvesting of this partial crop deposit. Theuninterrupted switching from the first operating mode to the secondoperating mode enables a change in the operating behavior of the cuttingunit 1, such that the cutter bar 6 is then operated in a flexiblemanner.

In a first method step, the sensor bands 14 are regulated to a minimumtarget value. Subsequently, the cutter bars 6 are released through acorresponding activation of the actuator element 6, i.e. the hydrauliccylinder 12. Upon overcoming the second threshold value for the pressureto which the hydraulic cylinders 12 on the support arms 11 aresubjected, the first sensor assembly 13 is deactivated by the controldevice 50, i.e. signals recorded by the first sensor assembly 13 are nolonger processed by the control device 50. Instead, the second sensorassembly 17 is activated, i.e. signals provided by this sensor assembly17 representing a change in distance through the deflection of thecutter bar 6, are processed by the control device 50 for adjusting theheight. A switching from the first operating mode to the secondoperating mode is also useful, when, due to the condition of the ground,or the ground contour, harvesting with a rigidly operated cutter bar 6over the entire working width of the cutting unit 1 is not possible.

Upon leaving the region of the crop deposit, the operator switchesoperating modes again. In that the target value for the sensor bands 14returns again to the originally set cutting height, the uninterruptedtransition from the use of the second sensor assembly 17 back to thefirst sensor assembly is initiated. At the same time, the cutter bar 6is again tensioned through an activation of the actuator element, i.e.through pressure applied by the hydraulic cylinder 12, such that it canbe operated rigidly.

Another aspect of the method according to the invention is that with anoperation in the second operating mode, or third operating mode, when aheight position of the cutting unit 1 above the working position isreached, as is the case, for example, at headlands, or through a manualraising of the cutting unit 1, the control unit 50 automaticallyactivates the actuator element such that the cutter bar 6 is operatedrigidly. This ensures an optimal, or minimal, spacing between the reeland the cutting unit table, and allows the reel to optimally support theharvest flow. This function also supports the replacement of theattachment in the crop, because the cutter bar 6 is first released justabove the ground through the appropriate activation of the actuatorelement by the control device 50, i.e. it is again operated flexibly,which is detected by means of the first sensor assembly 13. As a result,the crop lifters are placed on the ground at the correct angle, insteadof at a steep angle, which would be obtained if the cutter bar 6 werereleased immediately, which would expose the crop lifters to the risk ofdamage when being placed back in the crop.

A flow chart illustrating possible operating states and transitionsbetween them is depicted in FIG. 4. The numeral 31 indicates an initialstate of the cutting unit 1, in which the cutter bar 6 is operatedrigidly. The cutting unit 1 is operated in the first operating mode. Themaintaining of the cutting height, or the distance of the cutting unit 1to the ground, is monitored by means of the sensor bands 14 of the firstsensor assembly 13.

The numeral 32 indicates a state of the cutting unit 1 in which thecutting unit 1 is switched to the second operating mode, in which thecutter bar 6 is operated flexibly. For this, the actuator element isactivated by the control unit 50 such that the hydraulic cylinder 12 issubjected to a hydraulic pressure that is lower than the secondthreshold value. In this state 32, the maintaining of the cutting heightis controlled or regulated based on the changes in the distance to theground determined by means of the first sensor assembly 13.

The numeral 36 indicates a transition step from the first state 31 tothe second state 32, which is initiated as a function of the targetvalue for the cutting height regulation that has been set. As hasalready been explained above, the setting of a minimum target value forthe sensor bands 14 results in the initiation of the transition from thefirst operating mode to the second operating mode.

The numeral 37 indicates a transition step from state 32 to state 31,which is initiated as a function of the target value that has been setfor the cutting height regulation, or alternatively, by the raising ofthe cutting unit 1 above the working position. The transition step 37from the second operating mode to the first operating mode thus takesplace through the change in the target value of the cutting heightregulation from a minimum target value to the target value set for thefirst operating mode, for the cutting height or the manual removal ofthe cutting unit 1.

The numeral 33 indicates the state of the cutting unit 1 in which thecutter bar 6 is operated in accordance with the second operating mode,wherein the height control is carried out by means of the second sensorassembly 17. In the transition step 38, the actual value of thehydraulic pressure the hydraulic cylinders 12 of the support arms 11 aresubjected to is monitored by the control device 50 for this. Uponexceeding the second threshold value for the pressure the hydrauliccylinders 12 are subjected to, the first sensor assembly 13 isdeactivated by the control device 50, and the second sensor assembly 17is activated.

The numeral 34 indicates the state of the cutting unit 1 in which thecutting unit 1 is operated in another operating mode. In this otheroperating mode, the cutting unit 1 is raised manually by an operator.This operating mode may be employed upon reaching a headland.

The numeral 39 indicates a transition step from state 33 to state 34,which is initiated with the raising of the cutting unit 1. According tothis transition step 39, the exceeding of a threshold value for theactual value of the cutting height is monitored by the control device50. When the threshold value for the cutting height is exceeded,another, time-dependent threshold value is monitored by the controldevice 50. The control device monitors how long the threshold value forthe cutting height is exceeded.

If this time-dependent threshold value is likewise exceeded, atransition step 40 is introduced by the control device 50. The cuttingunit 1 is switched to the first operating mode in accordance with state31. For this, the actuator element is activated accordingly by thecontrol device 50, in order to operate the cutter bar 6 rigidly.Moreover, the automatic deactivation of the second sensor assembly 17and activation of the first sensor assembly 13 by the control device 50take place. The transition step 40 is controlled in a position-dependentand time-dependent manner.

The numeral 41 indicates a transition step from the state 34 to thestate 33, which is initiated after raising the cutting unit 1 when theraising of the cutting unit 1 does not take longer than the perioddefined by the time-dependent threshold value. There is no change inoperating modes during the transition step 41.

The numeral 35 indicates the state of the cutting unit 1 in which thecutting unit 1 is operated in another operating mode. In this otheroperating mode, the cutting unit 1 is manually lowered by an operator.This operating mode may be employed after driving through a headland,before the cutting unit 1 is placed back in the crop that is to beharvested.

The numeral 42 indicates a transition step from state 31 to state 35,which is initiated with the manual lowering of the cutting unit 1.According to this transition step 42, the control device 50 monitors theexceeding of a threshold value for the actual value of the cuttingheight while the cutting unit 1 is lowered manually.

When state 35 is reached, another time-dependent threshold value ismonitored by the control device 50. The control device 50 monitors howlong the cutting unit remains below the threshold value for the cuttingheight. If the value likewise falls below this time-dependent thresholdvalue, a transition step 44 is introduced by the control device 50. Thecutting unit 1 is switched from the first operating mode according tostate 31 to the second operating mode according to state 33. For this,the actuator element is activated accordingly by the control device 50,in order to operate the cutter bar flexibly. Moreover, the automaticdeactivation of the first sensor assembly 13 and activation of thesecond sensor assembly 17 by the control device 50 takes place. Thetransition step 44 is likewise controlled in a position- andtime-dependent manner.

The numeral 43 indicates a transition step from state 35 back to state31, which is initiated after lowering the cutting unit 1 when thelowering of the cutting unit 1 does not take longer than the perioddefined by the time-dependent threshold value. The operating mode is notchanged during the transition step 43.

Fundamentally, this method can also be used when the raising andlowering of the cutting unit 1 is carried out automatically. Theentering and exiting a headland, for example, can be determined by meansof a position location system, such that the switching between theoperating modes can take place automatically.

List of Reference Symbols  1 cutting unit  2 main frame  3 middlesection  4 side section  5 conveyor  6 cutter bar  7 belt  7a conveyorbelt  8 feed device  9 feed roller 10 feed channel 11 support arm 12hydraulic cylinder 13 first sensor assembly 14 sensor band 15 bearingpoint 16 pivot axis 17 second sensor assembly 18 shaft 19 console 20lever assembly 21 step 22 step 23 step 24 step 31 state 32 state 33state 34 state 35 state 36 transition step 37 transition step 38transition step 39 transition step 40 transition step 41 transition step42 transition step 43 transition step 44 transition step

The invention claimed is:
 1. A method for operating a cutting unit witha rigidly or flexibly operated cutter bar, depending on harvestconditions, comprising: operating the cutting unit in at least one of afirst operating mode or a second operating mode, wherein the firstoperating mode uses a first sensor assembly for operating a cutter barof the cutting unit rigidly to be at a predefined height setting over aground, wherein the second operating mode uses a second sensor assemblyfor operating the cutter bar of the cutting unit flexibly so that thecutter bar is guided to follow a contour of the ground while a cuttingframe of the cutting unit is guided at a predetermined distance from theground; determining at least one aspect of operation, the at least oneaspect of operation comprising a height position of at least a part ofthe cutting unit or a location of the cutting unit based on a positionlocation system; and automatically switching, based on the at least oneaspect of operation comprising the height position of the at least apart of the cutting unit or the location of the cutting unit, betweenone of the first operating mode and the second operating mode andanother of the first operating mode or the second operating mode,wherein depending on the selected operating mode, output from the firstsensor assembly or the second sensor assembly is used for control of thecutter bar without interruption of the operation of the cutting unit. 2.The method according to claim 1, further comprising calibrating thefirst sensor assembly and the second sensor assembly independently ofthe selected operating mode.
 3. The method according to claim 1, furthercomprising calibrating the first sensor assembly and the second sensorassembly independently of one another.
 4. The method according to claim1, wherein, responsive to determining that the cutting unit is operatingabove the predefined height setting, automatically switching tooperating the cutting unit with the rigid cutter bar independently ofthe selected operating mode.
 5. The method according to claim 4, whereinresponsive to determining that the cutting unit is operated with theflexible cutter bar above the predefined height setting for greater thana time-dependent threshold, automatically switching to the firstoperating mode for operating the cutting unit with the rigid cutter bar.6. The method according to claim 1, wherein, responsive to determiningthat the cutting unit is operating below a threshold value for thepredefined height setting of the cutter bar, automatically switching tooperating the cutting unit with the flexible cutter bar, independentlyof the selected operating mode.
 7. The method according to claim 6,wherein responsive to determining that the cutting unit is flexiblyoperating with the cutter bar below a threshold value for the predefinedheight setting for greater than a time-dependent threshold,automatically switching to the second operating mode and using thesecond sensor assembly for controlling the cutting unit.
 8. A combineharvester that can be operated, in accordance with the method ofclaim
 1. 9. The method according to claim 1, wherein the first sensorassembly comprises a mechanical ground sensing device.
 10. The methodaccording to claim 1, wherein the second sensor assembly detects adistance to the ground.
 11. The method according to claim 1, wherein thecutting unit comprises a grain cutting unit.
 12. The method according toclaim 2, wherein the calibration of the first sensor assembly and thesecond sensor assembly is performed sequentially.
 13. The methodaccording to claim 1, wherein the at least one aspect of operationcomprises a height position of at least a part of the cutting unit. 14.The method according to claim 13, wherein, responsive to manuallyraising the cutting unit, automatically switching to the first operatingmode so that the cutting unit operates with the rigid cutter bar. 15.The method according to claim 1, wherein determining the at least oneaspect of operation comprises determining a location of the cutting unitbased on a position location system; and wherein automatically switchingis based on the location of the cutting unit.